1. Field of the Invention
Exemplary embodiments of the present invention relate to a ray tracing method; and, more particularly, to a method for conducting 3D preprocessing for ray tracing so that 3D ray tracing simulation, which is used to predict radio propagation characteristics, is performed efficiently at an improved analysis speed.
2. Description of Related Art
Current telecommunication systems subdivide the coverage into a number of cells, each of which is allocated different frequencies to reduce interference with neighboring cells. Cells are largely divided into two types: macrocells and microcells. Macrocells cover areas having a radius of a number of kilometers or tens of kilometers, and it is theoretically impossible to model many propagation obstacles within the macrocells. This means that radio propagation characteristics cannot be determined but by statistical prediction methods based on experiments.
Microcells, in contrast, have a cell radius of 1 km or less, and it is possible to mathematically model various buildings, which are typical propagation obstacles within the cells, and to theoretically predict the path loss of radio waves. Specifically, the soaring number of telecommunication service subscribers in urban areas is making it more and more important to develop models to predict radio propagation characteristics in microcells.
It has also been requested in line with the recent increase in the number of personal telecommunication subscribers to study radio propagation characteristics in microcells/picocells, which have a radius of 200-500 m, and to develop relevant models. Radio propagation characteristics in microcell/picocell systems have major differences, compared with current macrocells and quasi-macrocells, including low transmission antennas, low-level transmission output power, limitation of radio propagation distance imposed by buildings around transmission stations, and possibility of numerical modeling of propagation obstacles within cells.
Such striking differences have the following result: Base station antennas are as tall as streetlights in microcells/picocells. In other words, they are lower than neighboring buildings. This causes severe attenuation. Furthermore, diffraction of radio waves by edges of buildings affects the receiving side to a larger extent than diffraction by rooftops.
Microcells/picocells in urban environments, which have cell radius of hundreds of meters, exhibit widely varied propagation characteristics depending on the structure. In other words, the size and material of buildings, shape and width of roads, traffic, etc., all of which constitute the cell structure, vary the propagation environments (i.e. site-specific). Therefore, there exists a need for models for more precise prediction in microcells/picocells, and such models are commonly based on ray tracing.
The ray tracing refers to a technique of tracing the path of rays reaching mobile stations to extract the received power, rms delay time spread, etc., which are crucial to wireless network design.
Ray tracing techniques include an approach based on image theory, an approach based on ray launching, and an approach combining both of them. The approach based on image theory requires a short calculation time, but makes it difficult to extend the prediction structure. The approach based on ray launching enables extension of the prediction structure, but requires a long calculation time and has poor prediction accuracy.
Therefore, it is necessary to select a suitable ray tracing method based on cell structures constituting the propagation environments. However, conventional approaches have limitation in that the number of necessary calculations increases in proportion to the number of structures, and the analysis of simulation to predict propagation characteristics becomes slower noticeably.
Specifically, the prediction method based on ray launching uses actual building data to calculate every propagation path possible, and the resulting propagation model is very accurate. However, prediction of every propagation path possible is limited, and it takes a long time to predict as many propagation paths as possible.
Therefore, there is a need for more efficient analysis at a higher speed in connection with ray tracing in urban environments, where the complexity of ray tracing increases in proportion to the number of structures.